A liquid crystal display device is a display device including a pair of substrates (for example, an active matrix substrate and a color filter substrate) facing each other via a liquid crystal layer. With the spread of use of liquid crystal display devices, the performance of the liquid crystal display devices has been improved.
In order to improve the display quality of the liquid crystal display device, it is necessary to precisely control the thickness of the liquid crystal layer (hereinafter also referred to as a cell gap). Especially, in a large-sized liquid crystal display device which has become widely utilized in recent years, it is necessary to control the cell gap uniformly over a very large area.
The cell gap is usually controlled by spacers arranged between the pair of substrates. As the conventional spacer, a particle-shaped spacer (for example, a plastic bead) has been used, and these spacers are used by being dispersed on the substrate. However, the positions at which the spacers are arranged cannot be controlled by the system of dispersing the spacers, such as plastic beads. This has become a cause of disturbing the alignment of liquid crystal molecules in a liquid crystal layer used as a display region. When there is a region in which the alignment of liquid crystal molecules is disturbed, the region is visually recognized as having display roughness. Further, when such spacers are used, the cell gap is varied due to the influence of recessions and projections on the substrate surface. In some cases, this has resulted in display unevenness.
To cope with this, in recent years, there has been adopted a method in which column-shaped spacers are formed between the substrates by a photolithography process using a photosensitive material. The spacer formed by this method is also referred to as a columnar spacer (photo spacer). However, there are various problems also in the case of forming the columnar spacers, and hence, for example, the following studies have been made.
When the columnar spacer is locally pressed from the outside, the amount of deformation of the cell gap differs according to the magnitude of the pressing force. The cell gap is also deformed by the atmospheric pressure and the weight of the substrate itself, and tends to be reduced at a position closer to the center of the substrate and to be increased at a position closer to the outer side of the substrate. To cope with this, a method has been tried in which the deformation ratio of the cell gap with respect to the compressive stress is made different for each of the columnar spacers so that the cell gap is uniformly maintained (see, for example, Patent Literature 1).
Further, since the alignment of liquid crystal molecules is disturbed around the columnar spacer, a black matrix is provided on the region where the columnar spacer is formed, and thereby the region is set as a non-display region. When a columnar spacer is formed by using the photolithography process, an alignment mark is provided at a desired position on a substrate, and on the basis of the alignment mark, the columnar spacer is provided so as to overlap with the black matrix. However, there is a case where the alignment mark is shifted, so that the columnar spacer, which is to be formed to overlap with the black matrix, is formed at a position overlapping with a color filter. For this reason, an attempt has been made in which the width dimension of the columnar spacer is adjusted to a desired condition corresponding to the width dimensions of the black matrix and the color filter so that, even when the alignment mark is shifted, the deterioration of display quality is prevented (see, for example, Patent Literature 2).
Further, an attempt has been made in which the stability of retaining the cell gap is improved in such a manner that, when a columnar spacer is formed in a region making no contribution to the display, the surface of the columnar spacer, which faces a light shielding layer, is made flat, and also the surface of the light shielding layer, which faces the columnar spacer, is also made flat, and that the area of the surface of the light shielding layer is formed larger than the area of the surface of the columnar spacer (see, for example, Patent Literature 3).